FIG. 13 is a front cross-sectional view illustrating a configuration of a representative embodiment of a conventionally suggested thermostat device 101, and illustrates a state in which a main valve 121 is opened to a cylindrical valve seat 111 the thermostat device 101. Description will be made on the assumption that the thermostat device 101 is installed on a cooling system circuit that circulates a liquid coolant through a bypass passage and a radiator of an automobile engine.
The thermostat device 101 is used by being fixed into a thermostat housing 103 in which a liquid coolant passage room 103d where a liquid coolant flows in and out through various ports 103a, 103b, and 103c is formed, and includes a cylindrical valve seat 111, a main valve 121 which closes the cylindrical valve seat 111 by being caused to approach the inside of the cylindrical valve seat 111, and a thermosensitive movable body 131 which drives the main valve 121 in a vertical direction of FIG. 13 by detecting a temperature of a liquid coolant.
In addition, the thermostat device 101 further includes a housing 133 of which both sides are fixed to a flange portion 113 provided in a flange shape at an external side of the cylindrical valve seat 111, and a piston shaft 135 of which a top edge is supported at the central side of the housing 133 and of which a bottom end side is received in the thermosensitive movable body 131. In addition, the thermostat device 101 includes a frame 137 of which an upper side is fixed to the flange portion 113 of the cylindrical valve seat 111, and a main spring 139 which is provided between the main valve 121 and a lower side of the frame 137 and is pressed against the main valve 121 to be pushed upward.
As illustrated in FIG. 13, on the main valve 121 of the thermostat device 101, a convex portion 123d having a convex shape at an upper side with respect to an upper surface of a circumference edge portion 123c is formed at an inner circumference side of the circumference edge portion 123c in a valve body 123 made of metal and having a predetermined shape. A circular elastic body 125 made of elastic synthetic rubber and the like is adhered to an outer peripheral surface 123e of the convex portion 123d, and an approach portion 124 approaching the inside of the cylindrical valve seat 111 when the valve is closed includes the circular elastic body 125 and the convex portion 123d. An outer peripheral surface of the approach portion 124 which is an outer peripheral surface of the circular elastic body 125 is provided with a circular sealing lip 127 which is elastically pressure-welded to an inner peripheral surface 111a of the cylindrical valve seat 111 when the main valve 121 is closed.
In the thermostat device 101 configured as described above, a thermal expansion body sealed inside of the thermosensitive movable body 131 thermally contracts when a temperature of a liquid coolant flowing into a neighborhood of the thermosensitive movable body 131 is lower than a predetermined temperature, and the piston shaft 135 is pushed back from an illustrated state in the thermosensitive movable body 131 by a force with which the main spring 139 is pressed against the main valve 121 in a valve closing direction. In this way, in a state in which an upper surface of the circumference edge portion 123c of the main valve 121 comes into contact with a lower surface of the flange portion 113 of the cylindrical valve seat 111 and stops after the main valve 121 and the thermosensitive movable body 131 move in a valve closing direction, the main valve 121 is closed with respect to the cylindrical valve seat 111. In this case, the circular sealing lip 127 is elastically pressure-welded to the inner peripheral surface 111a of the cylindrical valve seat 111, and thus a part where the circular sealing lip 127 is pressure-welded is sealed.
When a temperature of a liquid coolant flowing into a neighborhood of the thermosensitive movable body 131 is greater than or equal to the predetermined temperature, the thermal expansion body sealed inside of the thermosensitive movable body 131 thermally expands and pushes out the piston shaft 135. Accordingly, the thermosensitive movable body 131 and the main valve 121 move downward in FIG. 13, and the circular sealing lip 127 is separated from the inner peripheral surface 111a of the cylindrical valve seat 111. Thereafter, as illustrated in FIG. 13, the main valve 121 is opened to the cylindrical valve seat 111, and the liquid coolant starts to circulate between the cylindrical valve seat 111 and the valve body 123.
Thereafter, the piston shaft 135 expands and contracts due to a thermal expansion and a thermal contraction of the thermal expansion body in the thermosensitive movable body 131 according to an amount of change in temperature of the liquid coolant, which causes the main valve 121 and the thermosensitive movable body 131 to move.
Incidentally, in the thermostat device 101 described above, the circular sealing lip 127 of the main valve 121 is provided along a circumferential direction without changing a position in a vertical direction on the drawing, and the circular sealing lip 127 tends to be concurrently separated from the inner peripheral surface 111a of the cylindrical valve seat 111 throughout the whole circumference of the circumferential direction when the valve is opened. For this reason, for example, when a temperature of a liquid coolant circulated through the inside of an engine rapidly increases, and a differential pressure of both upper and lower sides of the main valve 121 by a water pump is great, a liquid coolant at a lowered temperature within a radiator rapidly flows in from a downside to an upper side on the drawing of the main valve 121 immediately after the valve is opened, and a liquid coolant at a lowered temperature immediately flows in an engine cooling circuit.
Accordingly, when a temperature of a liquid coolant within a cooling circuit causes an undershoot, and the main valve 121 is closed as a reaction, the temperature of the liquid coolant causes an overshoot this time. When this phenomenon is repeated, hunting may occur. In particular, the hunting may occur due to an increased temperature width when an outside temperature is low in winter season and the like. As a result, a thermal stress caused by a thermal change has a significantly negative effect on the engine.
Therefore, to resolve a problem regarding the hunting described above, various technologies that improve a configuration of the cylindrical valve seat 111 or the main valve 121 have been proposed (for example, see Patent Literatures 1 and 2).
In a thermostat device disclosed in Patent Literature 1, a notch as an opening groove having a letter V shape in which a liquid coolant passage is gradually narrowed from an upper side of a main valve toward a lower side thereof is formed at several places of a circular elastic body provided in a perpendicular valve portion of the main valve. In addition, in the thermostat device disclosed in Patent Literature 1, the circular elastic body is adhered up to a horizontal valve portion of the main valve, and a circular protrusion is provided so that the circular elastic body may approach and be away from a lower surface of a horizontal valve seat portion of a cylindrical valve seat.
In the thermostat device configured as above, a small amount of liquid coolant is circulated through the notch in an initial stage of valve opening after the main valve slightly moves from a valve closing state, and it is operated such that a flow rate of the liquid coolant gradually increases as the main valve moves from the state in a valve opening direction.
In a thermostat device disclosed in Patent Literature 2, a circumference edge portion of a horizontal portion of a main valve is formed to be bent toward a side of a horizontal valve seat of a cylindrical valve seat, and a circular elastic body is adhered up to a horizontal portion of the main valve. In the thermostat device, a circular protrusion is provided so that the circular elastic body may approach and be away from a lower surface of the horizontal valve seat of the cylindrical valve seat, and a water passing hole is formed at the horizontal valve seat of the cylindrical valve seat.
In the thermostat device configured as above, a circular sealing lip of the circular elastic body is caused to come into contact with an inner peripheral surface of the cylindrical valve seat when the valve is closed, and the circular protrusion of the circular elastic body is caused to come into contact with the horizontal valve seat of the cylindrical valve seat. When the valve is initially opened, only the circular protrusion of the circular elastic body is separated from the horizontal valve seat of the cylindrical valve seat, a small amount of liquid coolant passes through the water passing hole of the horizontal valve seat, and a flow rate at a front and a rear of the main valve and the cylindrical valve seat is controlled at a small flow rate. When the main valve further moves in the valve opening direction from the state, and the circular sealing lip of the circular elastic body is separated from the inner peripheral surface of the cylindrical valve seat, a liquid coolant starts to circulate between the circular sealing lip and the cylindrical valve seat, and a flow rate of the liquid coolant increases in earnest.